The formation of flanges or bellows in plastic tubes is well known. Plastic flanged tubes are used in a variety of applications including gas tank vents. Heretofore, the flanges or bellows in plastic tubes have been formed either by blowing out a portion of the tube from inside or by forming the flange in a mold.
In the blowing out method, a plastic tube is preheated at precise points. Then pressure is applied at the inside wall of the tube at the preheated points to cause the wall to stretch and bulge and eventually form a flange.
One consequence of this method is that the end of the flange thus formed is very thin walled. Its thickness is less than that of the original tube wall because it only comprises a stretched portion. Thus, the flange is a weak point in the tube structure.
Gas tank vents of polyethylene tubing are formed with retaining flanges or rims by which they are mounted. Such vents are subject to swelling or bending upon exposure to gasoline. If the rims won't accommodate such bending or swelling, they are subject to failure.